A new approach to distinguishing multiple phases of metamorphism and deformation: application to the Northeastern Appalachian
Kim, Hyeong Soo (2001) A new approach to distinguishing multiple phases of metamorphism and deformation: application to the Northeastern Appalachian. Geosciences Journal, 5 (1). pp. 65-84.
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Garnet, staurolite and aluminosilicates in St, Ky, and Sil zones on the northeastern flank of the Pelham Dome, Massachusetts, USA show microstructural and petrographic features suggesting multiple episodes of mineral growth. Sigmoidal, staircase, spiral and differentiated crenulation cleavage inclusion trail geometries as well as other textural truncations are preserved in both garnet and staurolite indicating these porphyroblasts developed by at least three periods of growth. These periods were distinguished using the trends and relative timing of the foliation inflexion/intersection axes (called FIA) preserved as inclusion trails within porphyroblasts. A total of 122 FIA trends were determined from garnet, staurolite, biotite and plagioclase porphyroblasts. FIA trends of garnet and staurolite are divided into four FIA sets as follows; NW-SE (set A), NE-SW (set B), E-W (set C) and NNW-SSE to NNE-SSW (set D). The relative timing of each FIA set was determined from porphyroblasts containing two or three different FIA trends consistently developed from core to rim. The succession from the oldest to youngest FIA sets are designated A, B, C and D. The variation of FIA trend populations around the Northfield syncline may be also attributed to difference in metamorphic grade and fold geometry, and may have been controlled by modal changes in metamorphic minerals involved in garnet/staurolite growth and consumption reactions accompanying the multiple deformation and metamorphic events. Based on Temperature—time (T—t) geochronological data and late-Paleozoic tectonic model in the study area, garnet and staurolite porphyroblasts containing four FIA sets may have developed during Devonian-Mississipian, and the matrix may have remetamorphosed during Permian.
|Item Type:||Article (Refereed Research - C1)|
|Keywords:||deformation; metamorphism; Northeastern Appalachian; garnet; FIA; staurolite|
|Date Deposited:||11 Dec 2010 00:31|
|FoR Codes:||04 EARTH SCIENCES > 0403 Geology > 040304 Igneous and Metamorphic Petrology @ 100%|
|SEO Codes:||97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%|